Cognition and behavior: Autism brains similar in girls and boys

Hot spot: Brain imaging implicates a region involved in emotion processing in girls with autism.

Girls with autism have more brain matter than do either controls or girls with other developmental disabilities, according to a study published 27 August in Neuroimage¹. This defect is particularly pronounced in the left superior frontal gyrus, a region in the medial prefrontal cortex that is responsible for higher-order cognitive function.

The results suggest that brain matter abnormalities reported for males with autism also exist in females with the disorder.

Several studies have shown that children with autism have macrocephaly, abnormally large brains that begin to taper in size after they reach 2 years of age. Studies using structural magnetic resonance imaging (MRI) have reported abnormalities in certain brain regions in both gray and white matter, which contain the cell bodies and connecting processes of neurons, respectively.

A study published earlier this year found that postmortem brains of children with autism have more neurons in the dorsolateral and medial prefrontal cortex compared with controls.

However, because autism is four times more common among males than females, imaging studies often omit females. Some studies have also reported male- or female-specific brain features, suggesting that the brain overgrowth seen in boys with autism may not apply to girls with the disorder.

In the new study, researchers used structural MRI and support vector analysis, a computerized method that finds patterns in data, to study the brains of 38 girls with autism and 38 age-matched female controls. Half of each group has an intelligent quotient (IQ) higher than 70, whereas the other half has developmental disabilities.

Overall, girls with autism have about five percent more gray matter than do controls, irrespective of age and IQ, the study found. Specifically, girls with autism have more gray matter in the superior frontal gyrus, a brain region implicated in autism. This region is responsible for several cognitive functions, including emotion processing and theory of mind, the ability to understand others’ intentions.

Compared with controls, girls with autism also have a slight increase in the volume of brain regions adjacent to the superior frontal gyrus. These are the right hemisphere and the right temporo-parietal junction, which are also involved in social behavior.

References:

1: Calderoni S. et al. Neuroimage Epub ahead of print (2011) PubMed